Pipe surface treating method for fuel cell system

ABSTRACT

A method of electro-polishing an inner surface and an outer surface of a multi-bending pipe by letting a current flow to a positive electrode and a negative electrode in an electrolyte is provided. A mesh net having a shape corresponding to an inner shape of the multi-bending pipe and formed of an insulating material and an internal electrode disposed within the mesh net are placed within the multi-bending pipe. An external electrode is placed outside the multi-bending pipe such that the inner surface and the outer surface of the multi-bending pipe are electro-polished by applying a negative electrode to the internal electrode and the external electrode and applying a positive electrode to the multi-bending pipe.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of priority to Korean Patent Application No. 10-2013-0167260, filed on Dec. 30, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a pipe surface treating method for a fuel cell system, and more particularly, to a method of electro-polishing surfaces of various pipes used in a fuel cell system, such as surfaces of multi-bending pipes.

BACKGROUND

In general, pipes used in a fuel cell system include pipes for various purposes such as a pipe for feeding a fluid to an electrode and a pipe for supplying cooling water.

Such pipes are mainly made of stainless steel having excellent physical and mechanical characteristics, for example, SUS316L which has excellent mechanical properties among various stainless steels.

Various by-products are deposited on an inner surface of the pipes made of a metal, such as stainless steel, due to the adhesion and surface reactions of the by-products. The pipes react with these by-products thereby damaging the pipes. To prevent such damage, in general, the outer and inner surfaces of the pipes are polished.

The pipes used in a fuel cell system are manufactured through cutting, bending, forming of an end of the pipe, electro-polishing and finishing of the pipe, etc.

Here, the electro-polishing process for a surface of a pipe is for reinforcing an anti-corrosion property and an ion elution degree of the pipe.

As shown in FIG. 4, for example, the pipe surface electro-polishing process is a process of placing a pipe 100 that is to be electro-polished in an electrolyte, disposing electrodes 110 at opposite sides of the pipe 100, and applying a positive current to the pipe 100 and a negative current to the electrodes 110 to polish a surface of the pipe 100.

However, the surface electro-polishing is for polishing only a surface of a pipe by using the electrical characteristics of an electrode for electro-polishing and a current, and thus, the surface electro-polishing is in fact not relevant to the inner surface of the pipe which contacts with a cooling water.

In case of using a multi-bending pipe, only the outer surface of the multi-bending pipe can be electro-polished due to the characteristics of current called “skin effect” (a current flows along the surface of a conductor).

Even when an electrode is separately manufactured to electro-polish the inner surface of the multi-bending pipe, electro-polishing becomes impossible if the electrode contacts a curved portion of the pipe. Thus, an electrode that can pass through a curved portion of a multi-bending pipe without contacting an inner surface of the pipe is required to polish the inner surface of the pipe.

SUMMARY

The present disclosure has been made in an effort to solve the above-described problems. An aspect of the present disclosure provides a pipe surface treating method for a fuel cell system in which a new type of surface treating method that can electro-polish an inner surface of a multi-bending pipe by combining a plastic mesh net through which a current cannot flow and a flexible electrode when a surface of a multi-bending pipe used in a fuel cell system is electro-polished. Thus, both an outer surface and the inner surface of the multi-bending pipe can be electro-polished to improve anti-corrosion property and ion elution degree, thereby increasing an electrical safety of a vehicle.

In accordance with an exemplary embodiment of the present disclosure, a method of electro-polishing an inner surface and an outer surface of a multi-bending pipe by letting a current flow to a positive electrode and a negative electrode in an electrolyte is provided. A mesh net having a shape corresponding to an inner shape of the multi-bending pipe and formed of an insulating material and an internal electrode disposed within the mesh net are placed within the multi-bending pipe. An external electrode is placed outside the multi-bending pipe such that the inner surface and the outer surface of the multi-bending pipe are electro-polished by applying the negative electrode to the internal electrode and the external electrode and applying the positive electrode to the multi-bending pipe.

The mesh net may be formed of a circular mesh net that is an insulating material.

The external electrode may have a shape corresponding to an outer shape of the multi-bending pipe and may be disposed along the outer surface of the multi-bending pipe in parallel to the outer surface of the multi-bending pipe.

The electrolyte may be obtained by mixing sulfuric acid, phosphoric acid, distilled water, and a platinum additive.

The mesh net may be formed of a flexible meshed electrode (copper wire) that is inserted into a bent portion of the multi-bending pipe.

The pipe surface treating method for a fuel cell system according to the present disclosure has the following advantages:

As an inner surface and an outer surface of a stainless steel (SUS304) pipe used in a fuel cell system can be electro-polished, an electrical safety of a vehicle can be improved by improving anti-corrosion property and decreasing ion elution degree, thus, reducing the manufacturing cost.

That is, an ion elution degree of a conventional product is 3.1 uS/cm, whereas an ion elution degree according to an exemplary embodiment of the present disclosure is 2.4 uS/cm, which is lower than that of the conventional product.

Further, since the price of a currently mass-produced SUS product with a diameter of φ19 mm, which is electro-polished, is about 22 US dollar per meter, but the price of the present disclosure with a diameter φ19 mm, inner and outer surfaces of which is electro-polished, is about 4 US dollar per meter, that is, about 84% of the price is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated by the accompanying drawings which are given hereinafter by way of illustration only, and thus are not limitative of the present invention.

FIG. 1 is a schematic diagram showing an electrode and an insulator used in a pipe surface treating method for a fuel cell system according to an embodiment of the present disclosure.

FIG. 2 is a schematic diagram for explaining the pipe surface treating method for a fuel cell system according to the embodiment of the present disclosure.

FIGS. 3( a)-3(c) show pictures depicting an electrode and an insulator used in the pipe surface treating method for a fuel cell system according to the embodiment of the present disclosure.

FIG. 4 is a schematic diagram showing a pipe surface treating method for a fuel cell system according to the related art.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing an electrode and an insulator used in a pipe surface treating method for a fuel cell system according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram for explaining the pipe surface treating method for a fuel cell system according to the embodiment of the present disclosure.

As shown in FIGS. 1 and 2, the pipe surface treating method is a method of effectively electro-polishing an inner surface of a multi-bending pipe 10 as well as an outer surface thereof, and allowing a current to flow between a positive electrode and a negative electrode in an electrolyte to electro-polish both the inner surface and the outer surface of the multi-bending pipe 10.

A pipe-shaped mesh net 11 has a shape corresponding to an inner shape of the multi-bending pipe 10 used in a fuel cell system, for example, straight line portions and bent portions of the multi bending pipe 10. An internal electrode 12 also has the same shape and is disposed within the mesh net 11.

The mesh net 11 is an insulator through which a current cannot flow, and a plastic mesh net may be used which is manufactured through injection-molding.

The internal electrode 12 may be formed of a flexible material, that is, a copper wire that can be inserted and moved along the bent portions of the multi-bending pipe 10. In particular, the internal electrode 12 has a length slightly larger than that of the mesh net 11.

The mesh net 11 may have a diameter large enough to be inserted into the multi-bending pipe 10, or the mesh net 11 may have a diameter large enough to be attached to the inner surface of the multi-bending pipe 10, such that the mesh net 11 is fixedly disposed in the multi-bending pipe 10.

The inner electrode 12 may have a diameter large enough to be attached to an inner circumferential surface of the mesh net 11. That is, an outer surface of the inner electrode 12 may be surrounded by the mesh net 11.

An external electrode 13 is provided for electro-polishing the outer surface of the multi-bending pipe 10.

The external electrode 13 may be disposed along the outer surface of the multi-bending pipe 10 in parallel to the multi-bending pipe 10 while having a shape corresponding to an outer shape of the multi-bending pipe 10. The external pipe 13 also may be a flexible copper wire.

FIG. 2 is a schematic diagram for explaining the pipe surface treating method for a fuel cell system according to the embodiment of the present invention.

As shown in FIG. 2, the multi-bending pipe 10 is disposed within an electrolyte container 14 filled with an electrolyte obtained by mixing a sulfuric acid, a phosphoric acid, distilled water, and a platinum additive to perform the surface electro-polishing method.

First, the internal electrode 12 and the mesh net 11 are inserted along an inner shape of the multi-bending pipe 10. The internal electrode 12 does not contact the multi-bending pipe 10 due to the mesh net 11 to be insulated.

The external electrode 13 is disposed outside the multi-bending pipe 10 and spaced apart from the multi-bending pipe 10 by a predetermined distance in parallel to the outer surface of the multi-bending pipe 10.

The multi-bending pipe 10 is directly put into the electrolyte container 14 filled with an electrolyte in the state in which the internal electrode 12, the mesh net 11, and the external electrode 13 are disposed inside and outside the multi-bending pipe 10. Thereafter, a positive electrode of a rectifier 15 is connected to the multi-bending pipe 10, and a negative electrode of the rectifier 15 is connected to the internal electrode 12 and the external electrode 13. Then, the electro-polishing is performed by applying a current to the rectifier 15.

As a result, the inner surface and the outer surface of the multi-bending pipe 10 to be polished are melted in the electrolyte, in which current densities at protruding portions of the inner surface and the outer surface of the multi-bending pipe 10 are increased so that the protruding portions become flattened.

As shown in FIG. 3, the inner surface and the outer surface of the multi-bending pipe 10 can be treated to be uniform and clean.

In particular, in the case of stainless steel SUS 304 for a fuel cell system, the price is low but the anti-corrosion property is significantly low as compared with stainless steel SUS 316L. Also, the ion elution degree of SUS 304 is low that it cannot be applied to a vehicle when the conventional outer surface electro-polishing is applied. However, when electro-polishing is applied to both an inner surface and an outer surface of a pipe according to the present disclosure, the ion elution degree is lowered and the anti-corrosion property is improved while the low manufacturing costs are low, thus improving an electrical safety of the vehicle and reducing the cost.

The pipe surface treating method according to the present disclosure, the manufacturing costs are reduced, ion elution is lowered, and anti-corrosion property is improved by realizing a double-side electro-polishing technology for developing a low-priced pipe for a fuel cell system.

The pipe treating method according to the present disclosure also may be applied to a pipe used in a semiconductor cleaning process, as well as a pipe used in a fuel cell system. 

What is claimed is:
 1. A method of electro-polishing an inner surface and an outer surface of a multi-bending pipe by letting a current flow to a positive electrode and a negative electrode in an electrolyte, the method comprising: placing a mesh net having a shape corresponding to an inner shape of the multi-bending pipe and formed of an insulating material and an internal electrode disposed within the mesh net within the multi-bending pipe; placing an external electrode outside the multi-bending pipe; and applying a negative electrode to the internal electrode and the external electrode and applying a positive electrode to the multi-bending pipe such that the inner surface and the outer surface of the multi-bending pipe is electro-polished.
 2. The method of claim 1, wherein the mesh net is formed of a circular mesh net made of an insulating material.
 3. The method of claim 1, wherein the external electrode has a shape corresponding to an outer shape of the multi-bending pipe and is disposed along the outer surface of the multi-bending pipe in parallel to the outer surface of the multi-bending pipe.
 4. The method of claim 1, wherein the electrolyte is obtained by mixing sulfuric acid, phosphoric acid, distilled water, and a platinum additive.
 5. The method of claim 1, wherein the mesh net is formed of a flexible meshed electrode that is inserted into a bent portion section of the multi-bending pipe.
 6. The method of claim 2, wherein the mesh net is formed of a flexible meshed electrode that is inserted into a bent portion of the multi-bending pipe.
 7. The method of claim 1, wherein the multi-bending pipe is directly placed into an electrolyte container filled with the electrolyte in which the internal electrode and the mesh net are disposed inside and the external electrode is disposed outside the multi-bending pipe.
 8. The method of claim 5, wherein the flexible meshed electrode is a copper wire. 